On paper, the top two seeds from last season’s NFC playoffs are both improved heading into 2011. Consequently, the Atlanta Falcons have become somewhat of a trendy Super Bowl pick. But the Chicago Bears? They’re the team most are picking to finish right behind Detroit in the NFC North. In analyzing five key threads these teams share, we might understand why.

1. Receiver InfusionThomas Dimitroff realized that Atlanta’s offense was a playmaker short of being nearly unstoppable. So, the fourth-year general manager traded five premium draft picks to move up and select Alabama wideout Julio Jones sixth overall.

Jones is a great fit because he’s not only a dynamic downfield threat who also has the thickness to go inside, but thanks to his days in the Crimson Tide’s black-and-blue offense, he’s also a savvy downfield blocker. That’s important, as Falcons offensive coordinator Mike Mularkey has always had a predilection for power runs out of two tight-end/two back formations.

In Chicago, with a system built around downfield routes out of three-and four-receiver formations, offensive coordinator Mike Martz needed more firepower outside. Instead of reaching for an unproven wideout late in the first round, overpaying for free agents Santana Moss or Santonio Holmes or taking a risk on Braylon Edwards (attitude) or Plaxico Burress (rustiness), the Bears acquired Roy Williams after his star fully plummeted in Dallas.

Williams, a straight-line runner with big hands and feet, was never a good fit for the Cowboys’ shifty catch-and-run oriented system. But in the 28 games he played for Martz in Detroit, Williams produced 2,148 yards receiving. However, whatever optimism the Detroit success instilled was likely blown away by Williams’ dropped passes and admission to being out of shape this past August (candor has always been his Achilles heel).

Because the Bears refuse to admit that Devin Hester is merely a return specialist with modest slot receiving ability (i.e. NOT a starter), it was rising third-year pro Johnny Knox whom Williams supplanted in the lineup. Knox, who has superb speed and quickness and excellent chemistry with Jay Cutler, particularly in deciphering zone coverages, is eager to recapture his starting job (and thus, his leverage for a new contract in the near future). He will, if Williams continues to struggle. And the Bears’ passing game will essentially be right back in the same place it was a year ago.

The Falcons figure to clearly have an improved pass attack. The Bears are TBD.

2. Big meaty offensive linesTo put it politely, Atlanta’s and Chicago’s offensive lines both feature more size than athleticism. The lunch pail approach has worked great for the Falcons. They have a straightforward power-run offense that’s conducive to forming good chemistry up front. In the passing game (where a line’s athletic limitations get exposed), the Falcons rarely use more than three wide receivers, which makes an extra tight end or running back available to stay in and block. In short, the Falcons can bend their system for their offensive line.

The Bears, on the other hand, are more inclined to bend (or break) their offensive line for their system. Martz frequently has Cutler take seven-step drops, which only gives heavy-footed offensive tackle J’Marcus Webb, laterally stiff guard Chris Williams and the rest of the front more time to get beat in pass protection. Also, with the running back often being an important receiving option in Martz’s system, Bears linemen must shoulder more responsibility in blitz identification and pickup – an area in which they’ve struggled.

Hence, the 52 times Cutler was sacked last season.

3. The traditional 4-3 defense: evolve vs. resolveMike Smith was a classic zone-based 4-3 defensive coordinator in Jacksonville. But over his three seasons in Atlanta, he’s drifted away from vanilla Cover 2 tactics and towards more diverse blitzes and zone exchanges. Impressive considering he employs these tactics out of traditional base and nickel sets.

Lovie Smith was a classic zone-based 4-3 defensive coordinator in St. Louis. Over his seven years in Chicago, he’s ... remained a proponent of classic 4-3 zone-based defense.

The Bears are the only team that virtually still runs a fulltime strict Cover 2. They’ve made it work largely because they have two perfect linebackers for this scheme in Brian Urlacher and Lance Briggs. But as we’ll explore more in-depth another week, there are significant vulnerabilities to a Cover 2. Those vulnerabilities are why Smith and the Falcons have chosen to evolve.

4. The No. 2 defensive endArguably the best two defensive ends in the NFC are Julius Peppers and John Abraham. Both have devastating explosiveness off the edge and both can play the run (Peppers is by far the NFL’s best all-around run-stopping 4-3 end; Abraham is more finesse-oriented but is still underrated as a backside chaser).

What the Falcons learned last season is a pass-rush is incomplete without a second outside presence. Kroy Biermann is a very active run-defender, but he registered just three sacks in his debut season as a starter. So, Thomas Dimitroff spent $11 million (guaranteed) on free agent Ray Edwards, who each of the past two years in Minnesota posted at least eight sacks against frequent one-on-one blocking opposite Jared Allen. Edwards is also an adept all-around run-defender.

The Bears have a stalwart No. 2 pass-rusher of their own in Israel Idonije. Versatile enough to line up inside or outside, the ninth-year veteran tied Peppers for the team lead in sacks last season (eight). Idonije does not quite have Edwards’ quickness around the corner, but he’s one of the best in the league at executing stunts.

5. SafetiesOver the years, watching the Bears try out different young safeties in the starting lineup has been like watching Gilbert Brown try on outfits that don’t make him look fat. The Bears drafted Danieal Manning in ’06; Kevin Payne in ’07; Craig Steltz in ’08; Al Afalava in ’09; Major Wright in ’10 and Chris Conte in ’11.

All, with the exception of Conte, were given a shot at starting. And, assuming that newly signed Brandon Meriweather soon supplants Wright as the current first-string free safety, all were ultimately deemed unqualified.

The Falcons have taken a flier with young safeties, as well. The difference is theirs have succeeded. Thomas DeCoud, a third-round pick in ’08, started all 16 games each of the past two seasons. His instincts in coverage have improved and he’s a fast, firm open-field tackler.

His running mate, William Moore, a second-round pick in ’09, stayed healthy for the first time last season and showed genuine game-changing potential over 15 starts. Moore’s a fierce hitter who is developing in pass defense quicker than expected.